1. Field of the Invention
The present invention relates to an elastic extension device and a retractable pulling rod using the same, and in particular to an elastic extension device capable of assisting extension and retraction of a retractable pulling rod.
2. The Prior Arts
Presently, in order to facilitate dragging and lifting a luggage trunk, the pulling rod of a luggage trunk is designed to be retractable, having a plurality of sockets, such that the number of sockets to be pulled out while using depends on the user's requirement.
Refer to FIG. 1 for a conventional multi-section luggage trunk pulling rod of the prior art. As shown in FIG. 1, the multi-section luggage trunk pulling rod includes: an inner tube 10, an intermediate tube 12, an outer tube 14, a first positioning device 16, and a second positioning device 18. The inner tube 10 is provided and received in the intermediate tube 12, the intermediate tube 12 is sleeved in the outer tube 14, and the first positioning device 16 and the second positioning device 18 are disposed at the bottom ends of the inner tube 10 and the intermediate tube 12 respectively. Wherein, the lower ends of the inner tube 10, the intermediate tube 12, and the outer tube 14 are provided with a least a corresponding first fastening hole 20 in communication; while the upper ends of the intermediate tube 12, and the outer tube 14 are provided respectively with a second fastening hole 22. The structures of the first positioning device 16 and the second positioning device 18 are the same, both are composed of a sleeve seat 171, an action element 172, a compressible spring 173, and a positioning bead column 174. The top surface of the sleeve seat 171 is connected to the action element 172, the lower end of the action element 172 is provided with an action plate 175, and the compressible spring 173 is sleeved around the action plate 175. The end of the positioning bead column 174 is inserted into a slant slot hole 176 at the lower end of the action plate 175, so that the positioning bead column 174 is able to slide in the slant slot hole 176.
In operation, an action rod 24 controls the actions of the first positioning device 16, so that the first positioning device 16 is connected to the second positioning device 18. To be more specific, when the action rod 24 presses down the action element 172 of the first positioning device 16, the action plate 175 is moved downward, so that the compressible spring 173 is in a compressed state. Meanwhile the positioning bead column 174 is moved upward along the slant slot hole 176 on the action plate 175, so that the positioning bead column 174 is detached from the first fastening holes 20 of the outer tube 14, the intermediate tube 12, and the inner tube 10, and retracts inward into inner tube 10. Similarly, the positioning bead column 174 of the second positioning device 18 is detached sequentially from the first fastening holes 20 of the outer tube 14, the intermediate tube 12, and retracts inward into the intermediate tube 12, so that the inner tube 10 and intermediate tube 12 can be pulled and extended freely in the outer tube 14.
When a user pulls the inner tube 10 and the intermediate tube 12 upward, until the positioning bead columns 174 of the first positioning device 16 and the second positioning device 18 correspond respectively to the second fastening holes 22 of the outer tube 14 and the intermediate tube 12, such that the compressible spring 173 is restored elastically, to make the positioning bead column 174 move downward along the slant slot hole 176 on the action plate 175, so that the positioning bead column 174 extends and protrudes to position on the second fastening hole 22, in achieving extension of the pulling rod. In the same manner, the action rod 24 has only to be pressed again to control the first positioning device 16 to connect to the second positioning device 18, to proceed with retraction and positioning actions as shown in FIG. 1.
Though, through the structure mentioned above, the extension and retraction of the pulling rod can be achieved. However, in actual applications, the length of the positioning bead column 174 has to be designed to protrude and extend through the first fastening holes 20 of the inner tube 10, and intermediate tube 12, and the outer hole 14, and the positioning bead column 174 has to be retracted into the corresponding socket. For a retractable pulling rod exceeding three sockets, the positioning bead column 174 has to extend and position in, or retract and detach from the through the fastening hole on the socket. Yet, by doing so, the friction and resistance in operation is relatively large (requiring more efforts), so that in extending or retracting the rod, it can not be positioned and fixed smoothly, hereby resulting in unstable operations. Also, the structure design of the retractable pulling rod is restricted by the length of positioning bead column 174.
Therefore, presently, the design and performance of luggage trunk pulling rod of the prior art is not quite satisfactory, and it has much room for improvements.